The 1991 Clean Air Act mandates significant reductions in sulfur dioxide emissions from the burning of coal over the next decade. To comply with the 1991 Clean Air Act, coal-burning power plants will need to either use coal with a low sulfur content or install pollution control devices known as scrubbers to reduce the sulfur dioxide content in the emissions from the burnt coal.
The combustion and emission characteristics of a specific coal are a function of its BTU, water, and sulfur contents. Coal will optionally have a high BTU content, low water content, and low sulfur content. More specifically, coal having a high BTU content of 12,000-14,000 BTU/lb. is desirable. Coal having a water content that is substantially less than 20% by weight is desirable because water decreases the BTU content. Also, coal having a water content in excess of 20% by weight is expensive to transport because it requires substantially more coal to achieve the necessary BTUs, and a significant percentage of the commodity that is being transported is merely water.
The combustion and pollution characteristics of coal varies according to the region from which it is mined. Coal from the eastern United States generally has a BTU content of 12,000-14,000 BTU/lb., but these reserves also have prohibitively high sulfur contents. Coal from the western United States generally has an unacceptably low BTU content of only 8,000-10,000 BTU/lb. and an unacceptably high water content of 20% to 36% by weight, but these reserves have an acceptably low sulfur content. Additionally, large lignite reserves are located in North Dakota. Although lignite has an acceptably low sulfur content that can meet the Clean Air Act regulations, these reserves have a low BTU content of only 6,000 to 7,000 BTU/lb.
Solutions to overcome the shortcomings of the different types of coal have developed. Eastern coal is processed by micronizing the coal into small particles. Micronization entails grinding the coal into a very fine powder, and mixing the finely ground coal with a finely ground component of limestone. High-sulfur coal can be micronized to readily meet the Clean Air Act emission standards. Micronized coal has superior energy properties compared to other types of coals. Also, burning micronized coal results in a coal-ash by-product that has a high market value as a cement feedstock.
Western coal is generally processed by drying the coal creating briquets or fine particles of dried coal. Drying reduces the water content in the coal to acceptable levels, thereby increasing the BTU content. Western coal that has been dried and pulverized has a heat value of about 12,000 BTU/lb. and a water weight that is as low as 2% by weight.
In addition to Eastern and Western coal, lignite may also be used as a fuel in power plants. Lignite is a particularly dry, dusty substance. Lignite may also be dried or pulverized which makes it even dustier.
Making finely divided coal by micronization or pulverization, however, requires an extremely large capital investment in equipment. Pulverizers, for example, represent up to 20% of the total capital cost of the modern power plant. Micronizing is even more expensive than pulverizing. Consequently, it is desirable to centralize the equipment to micronize and pulverize coal at large coal collection sites, and subsequently transport the refined coal to the individual end users.
The transportation of finely divided coal, dried coal and/or lignite, however, involves significant handling and safety problems. These substances are subject to blowing out of existing open-topped rail cars because of their small particle size. This phenomenon, known as "blowout," results in a significant loss of coal and unacceptable environmental damage to people and property near rail lines. Finely divided coal, dried coal and/or lignite are also subject to spontaneous combustion when exposed to oxygen. Micronized coal, in fact, is not only spontaneously combustible, but highly explosive when exposed to oxygen. Therefore, a significant need exists to provide effective solutions to prevent blowout and spontaneous combustion in the transportation of finely divided coal, dried coal and/or lignite.
Current transportation devices and methods do not provide effective solutions to prevent blowout or spontaneous combustion during the transportation of finely divided coal. One ineffective method currently in use is water suppression. Water suppression entails simply spraying the top surface of coal-laden rail cars with water, but this method is unsatisfactory because the coal is still subject to blowout after the water evaporates within a few hours after it has been applied. Water suppression also exacerbates freezing problems that impact the efficiency of rail transportation. Another ineffective method is to place a tarp over a loaded coal car to prevent blowout. This method, however, is too expensive because it involves extensive labor. Moreover, these methods do not prevent spontaneous combustion because the coal is still exposed to oxygen.
Yet another ineffective suppression method is to spray the load of coal with polymers that act as a binding agent and form a film over the coal. Although this method prevents blowout, polymers are prohibitively expensive and create additional emission concerns when the coal is burned. Moreover, the coal may still be subject to spontaneous combustion or explosion because the polymers may not create an impermeable barrier to oxygen.
Finely divided coal, and other combustible commodities, have been transported in pneumatic tanker cars to maintain reduced oxygen levels to prevent blowout and spontaneous combustion. Hauling finely divided coal in pneumatic tanker cars, however, is not an efficient solution to the transportation problems of blowout and spontaneous combustion. First, pneumatic tanker cars are very expensive to build. Second, costly delays occur because finely divided coal cannot be rapidly loaded and unloaded using pneumatic tanker cars. Third, the cars cannot be used for back hauling anything, so they do not generate revenue for a railroad on both legs of a round trip. Fourth, the cars must be completely filled with an anaerobic gas before filling the cars with combustible materials. Lastly, pneumatic tanker cars do not provide a device for storing the highly combustible finely divided coal at the collection sites and user facilities. Therefore, the need exists to be able to adapt the existing fleet of coal cars to haul finely divided coal such as micronized or pulverized coal.
Several problems arise in adapting existing coal cars to haul finely divided coal. The most significant problem is that the existing containers which could encapsulate finely divided coal concentrate significant forces against the side walls of the rail cars as they move from side to side during transportation. Existing containers lack stability in current rail cars because they generally rest only upon the centersill extending longitudinally along the length of the car. Consequently, the centrifugal forces created during transportation cause existing containers to pivot over the top of the centersill and push against the outer side wall of the rail car relative to the centrifugal force. These forces against the side walls significantly stress the side walls and the cross members of the railcars reducing the useful life of the rail cars.
Another significant problem affecting the useful life of the rails cars is that the existing containers which could encapsulate finely divided coal also concentrate significant longitudinal forces against the internal cross braces. As a rail car accelerates or stops, the rail car will move at a different rate relative to the containers in the car. As a result, a longitudinal force will be created that acts upon the internal cross braces of the car. The internal cross braces, however, are not designed for such forces because bulk coal is generally flowable and does not concentrate forces on any specific structure in the rail car.
Typical collapsible container designs, such as Fabribin manufactured by American Fuel Cell and Coated Fabric Company, are not readily adaptable for use in coal rail cars because they merely rest on top of the internal centersill. An invention by the present inventor entitled "Rail Car Conversion Apparatus" relates to a device and method for handling Fabribin containers in transferring the forces away from the internal braces. In the rail car conversion apparatus invention, a large harness is adapted to fit on top of the side walls of a rail car, and a plurality of containers attached directly to this harness from individual attachment points. The rail car conversion apparatus invention, however, represents an inefficient and costly means to transfer forces away from the internal braces.
U.S. Pat. No. 4,909,156 issued to the present inventor, discloses a large, flexible bladder for use with open-top rail cars. This bladder includes a filling port positioned at the top of the car, and a discharge port positioned adjacent to the flow-control valve system carried on the underside of the car. This bladder, however, cannot be inserted or extracted from the rail car when it is full of material. Consequently, the bladder of the '156 patent cannot be rapidly loaded and unloaded at the mines and utilities, thereby resulting in unacceptable delays. Moreover, these bladders also do not provide any infrastructure for adapting the bladders to conform to the internal cross-members of the cars.
Utilization of finely divided coal has significant economic and environmental benefits. Currently, however, finely divided coal cannot be transported safely and economically using the existing coal car fleet. Therefore, the need exists to have a custom container, and method using such a container, that is readily adaptable to the existing coal car fleet to prevent blowout and spontaneous combustion during the transportation of finely divided coal.